Alternating current (ac) machines (e.g., PMSM machines) are extensively used vehicle traction applications. A PMSM machine controller controls operation of the PMSM machine. The controller produces ac control signals which are applied to the terminals of the PMSM machine.
PMSMs are used due to their power density, efficiency, torque capability, size, and wide constant power operating region. One of the most widely used rare earth magnets in PMSMs are neodymium-iron-boron (NdFeB) magnets. NdFeB magnets are candidates for PMSMs due to their energy density, and intrinsic coercivity (Hci). Unfortunately the NdFeB magnets have a low resistivity which can lead to eddy currents in the magnets. Also, NdFeB magnets intrinsic coercivity and residual flux density are dependent on temperature, and their value decreases as the temperature increases. Finally a back electromotive force (bemf) constant (λf) is directly proportional the residual flux density. In other words, as the temperature increases the bemf constant decreases.
Ambient temperature, machine operating speed (PM eddy current losses), current regulation quality and THD level, current magnitude and duration, and machine cooling are factors which affect rotor magnet temperature and, as a result, affect the bemf constant.